Xwavemeter



July 1, 1947. s. D.- LAVOIE WAVE METER OriginalFiled Sept. 24, 1941 5Sheets-Sheet l 1947' 1 s. D. LAVOIE Re. 22,894

WAVE METER Origifial Filed Sept'. 24, 1941 3 Shee ts-Sheet 2 v 45 I r nINVENTOR N D. LAVOIE l; Racism July 1, 1947. s. LAVOIE WAYE METER 3Sheets-Shet 3 Original. Filed Sept. 24, 1941 INNER LIVER lTcT,

I INVENTOR STEPHEN o mvoue wwe HIS AGENT Reissued July 1, 1947 WAVEMETERStephen D. Lavoie, Little Silver, N. J assig'nor to ManufacturersElectronic Developments, Inc., Morganville, N. J a corporation of NewJersey Original No. 2,349,440 dated May 23, 1944, Serial 'No. 412,102,September 24, 1941.

Application for reissue October 24, 1944, Serial No. 560,087

10 Claims. 1 The present invention relates to wave meters, and moreparticularly to instruments for measuring the wave length or frequencyof ultra-high frequency oscillations generated, for example, by anelectronic tube oscillator. It represents a modification of thestructure illustrated and described in my application for patent filedAugust 5, 1941, which maturedinto Patent No. 2,328,561 and myapplication for patent filed August 25, 1942, which matured into PatentNo. 2,355,683.

There are, in general, two ways of measuring frequencies or wave lengthsif the use of multivibrators and other auxiliary apparatus isdisregarded. These two methods may be classified as ((2) Transmissionline type, ('b) Coil and condenser type.

The usual method of measuring the frequency of an oscillator with thetransmission line type of wave meter is to couple the line'to theoscillator andobserve the change in the meter connected in the circuitof the oscillator as the line is shorted through maximum and minimumnodal points. A shorting bar is moved up and down the transmission line,shorting out successively adjacent points on the line. The impedance ofthe line is reflected back on the oscillator, and a the bar is movedback and forth through the maximum or minimum points the impedance ofthe oscillator outfit is changed. The meter is ordinarily placed in thegrid circuit of the oscillator to indicate grid current which will varyin accordance with the changes in the impedance of the transmissionline. This method will measure ultrahigh frequencies, but not veryaccurately, for the reason that the transmission line representsdistributed inductance and capacity so that the line responds not onlyto the basic frequency but also to multiples and submultiples thereof.The apparatus does not lend itself to rapid measurement and is large andcumbersome, requiring great care in making the determinations.

The coil and condenser type of wave meter, when designed and employed inthe ordinary manner, is limited as to the range of frequencymeasurement, and in general will give accurate results only up to a fewhundred megacycles, because a meter of this type employs an open form ofinductance and a condenser of the usual construction. It is apparentthat in a construction of this kind considerable leakage of currentthrough the condenser and coil is inevitable, so that a meter of thistype is completely unreliable in the ultra-high frequency wave band, forexample, between 300 and TOO-megacycles.

The improved wave meter, which will be describedpresently, is of thecoil-condenser type referred to above, but the structure has 'beensocompletely modified as to increase the frequency range at which highlyaccurate results are obtained. In the first place,'the coil structure,as modified, has little or noresemblanc'e to an ordinary wound coil,although providing the'inecessary inductive reactance. It has beenfound'th'at coils cf the o'rdinary'type cannot be satisfactorily builtat the present timewhioh havea s0-ca1led ratio 27rfL R sufficiently highto provide-the requisite sharpness of the frequency resonance curve.Secondly, the necessary inductance is provided without any appreciabledistributed capacity, and substantially all of the capacity whichcontrols the resonance frequency of the tuned circuit is lumped into asingle element.

The primary objectof the present invention'is to'provide an accurate,compact andcontinuously variable wave meterfor the ultra-high frequencyspectrum.

Another object is t'oprovide an'ultra-high frequency wave meter whichmaintains its accuracy of measurement without further calibration'overlong periods of time and preferably over the en'- tire operating life ofthe meter.

A further object is to provide an instrument of the type referred to,which is inexpensive,'se1fcontained, portable, is shielded, and whichhas the minimum number of'operating parts.

Another object is to provide an ultra-high frequency wave meter in Whichthe frequencies to which the meter accurately responds may be readilyadjusted over a relatively wide frequency range, and the measurement offrequency can be indicated directly in cycles persecond or in wavelength.

A still further object is to provide a Wavem'e'ter which can accuratelymeasure frequencies in a range above 300 meg'acycles, and the resonantcircuits of the meter will not respond to the effects of multiple andsub-multiple frequencies.

In still another aspect the invention comprises an ultra-high frequencymeter in which the ratio of reactance to resistance Q is exceedinglyhigh in order to assure a suflic'ient sharpness of the frequencyresonance curve from which the frequency indications are derived.

These objects are attained, in brief, by providing a meter whichoperates on the coil-condenser principle, employing maximum currentindications (as distinguished from null current), and

in which the variations in frequency response are obtained by changingthe effects of a lumped capacity. The inductance of the resonant circuitis provided without the use of an ordinary type of wound coil so thatleakage between turns and also distributed capacity are avoided. Thevariable lumped capacitance of the improved meter resides between therugged. casing of the meter and the plunger which is given areciprocatory movement of a positive and resettable character.

Other objects and features will be apparent from a reading of thefollowing specification together with the accompanying drawings.

In the drawings:

Figure 1 is a perspective view of the improved wave meter, which isillustrated as being contained in a box for carrying purposes.

Figure 2 is a section taken along the line 2-2 in Figure 1, and lookingin the direction of the arrows.

Figure 3 is a sectional view of the improved meter partly broken away.The section is taken along the line 33 in Figure 4.

Figure 4 is a sectional view taken along the line 44 in Figure 2, andlooking in the direction of the arrows.

Figure 5 is a perspective view of the wave meter unit and associatedgearing, the unit being broken away to show the internal parts.

Figure 6 is a fragmentary plan view of the anti-back lash gear formingpart of the actuating mechanism.

Figure 7 is a section taken through a portion of the back lash gear toshow the mechanism by which the back lash is eliminated.

Figure 8 is a small section taken along the line 8-8 in Figure 4, andshowing a slightly modifled optional structure.

Figure 9 is a diagrammatic layout of the circult.

Referring to the drawings, the ultra-high frequency wave meter embodyingmy invention comprises a heavy approximately rectangular metal housing(Figures 3, 4 and 5), preferably a one-piece aluminum castin integrallyclosed on all sides except one side, and the open side being closed by aheavy metal cover plate 2 secured thereto by means of the screws 3, orin any other suitable manner. The casting I, also the cover plate 2, hasa thickness of not less than 1 1:" so that the housing is of anextremely rusged character, permitting no bends, warping or otherrelative displacement between the sides and the cover plate.

One of the sides is provided with a threaded opening 4 which is adaptedto receive the screw shank 5 of an input connector 6. This connectortakes a generalcylindrical shape and terminates at the end remote fromthe threaded portion 5 in a threaded collar 1, provided with acountersunk bore 8 and adapted to receive a nut 9. The purpose of thenut will be explained presently. The input connector is provided with anaxial bore which receives a metal rod 5,.

extending into a larger stub portion II on the interior of the housingand at the opposite end terminates in a metal terminal l2, provided withfour quadrantal sections which give a compre sion effect to a leading-inconductor I4. The rod I is insulated from the cylinder 6 by suitablematerial, for example a plastic I of the polystyrene type. Materialwhich is known on the market as Amphenol may be used for this purpose.At the opposite side of the housing i there is an opening which receivesan insulating bushing l6, preferably of a plastic material, this bushingbeing adapted to receive a leading-out conductor H which carries anenlarged stub portion I8. The stub portions H and i3 preferably arearranged on opposite sides of the housing, and they should beproportioned to transfer sufiicient energy to and from the rescnantcircuit without detuning it when the characteristics of their externalassociated circuits are changed. A suitable proportion and arrangementis exemplified in Figure i.

The variable condenser is comprised essentially of a hollow cylindricalmember IS, the interior of which is machined to dimension, terminatingat the bottom (Figures 3 and 4) in a flanged base 2E! which is securedin any suitable manner to the lower side of the housing. The upper edgeof the cylinder l9 is given a curvilin ear shape in order to provide thevariations in changes of capacitance when the parts of the condenser aremoved with respect to one another. The movable portion of the condenseris constituted of a plunger 2| which is slidably received by a cylinder22, the latter being flanged at 23 and secured to the cover plate 2 bthe screws 24. There is a longitudinal groove 25 provided at one side ofthe cylinder and a screw 26, carrying a locknut 21, is extended throughthe cylinder 22 into the groove. The purpose of the groove and the screwis to assure that the plunger 2| has only a reciprocatory movementwithin the cylinder and positively cannot rotate.

The diameter of the plunger 2| is such that when extended it will moveinto the circular opening formed by the cylinder l9.

It is apparent that the plunger, also its groove 25, and the interior ofthe cylinder 22 are all machined to dimension and preferably polished.It is desirable to coat the plunger 2|, the interior of the cylinder l9and the two stubs H, H? with silver in order to provide a low resistancepath for the high frequency energy, in which case the body of theseelements may be formed of a higher resistance and cheaper metal, such asbrass.

The plunger 2| is given its reciprocatory motion by means of a threadedrod 28, this rodextending practically the entire length of the plungerin order to assure stabilit of support. For this purpose the plunger 2|is provided with an internal bore which is threaded to receive thethreads of the-rod 28. The rod is shouldered at its upper end, asindicated at 29, the shouldered portion being journalled in the coverplate 2 and extending outside of the housing to serve as a shaft onwhich a large anti-back lash driving gear 30 and a pinion 3| aremounted. The plunger 2| is provided at its upper end with a countersunkbore 32 which receives the lower end of a compression spring 33, thelatter bearing at its upper end against the under side of the coverplate 2. The purpose of the Spring is to apply a constant pressureagainst the plunger 2| and thereby prevent any lost motion due tocontinued use.

It is apparent that as the gear 33 is rotated, in a manner which will bedescribed presently, the rod 28 will be likewise rotated, causing theplunger 2| to be moved either upwardly or downwardly depending on thedirection in which the gear is rotated, and thus to increase or decreasethe distance d between the lower edge of the plunger and the nearestsurface of the cylinder IS. The capacity of the wave meter ispractically entirely concentrated in the space between the plunger 2|and the cylinder l9 so that variations of capacitance are obtained bymoving the plunger with respect to the cylinder. The gear 30 ispreferably constructed in such a manner as to eliminate all back lash,and the details of a preferred construction are shown in Figures 6 and'7.

The gear 30 is peripherally split into two sections 34, 35, each sectionbeing provided with a rectangular opening 36 which is adapted to receivea compression spring 31. One of the sections, for example 34, isprovided with a tab 38 which extends into the opening 36, for examplefrom left to right, as shown in Figure 6. The other section 35 isprovided with a similar tab 39 positioned at the opposite side from thetab 38, and also extending into the openin 36. These tabs constituteoppositely positioned pins for locating the ends of the spring 31, thearrangement being such that the compressional eiTects of the springserve to slide the gear section 34 with respect to the other section sothat the teeth of the respective sections are slightly out of line withone another. It is apparent that any looseness f fit between the teeth40 and teeth with which the gear meshes will readily be taken up by therelative movement between the gear sections 34, 35. The gear 30 isactuated by a pinion 4| which is journalled at the lower end in thecover plate 2, as indicated at 42, and is provided with a hub 43 at theupper end, the hub portion being extended as a small diameter shaft 44which i provided with a handoperated wheel 45. The shoulder between theshaft 44 and the hub 43 abuts a metal plate 46 which is separated fromthe cover plate 2 by means of the spacers 41. Thus by turning the handwheel 45 it is possible to cause a reciprocatory motion of the plunger2! through the pinion 4|, anti-back lash gear 39, and the threaded rod28.

The pinion 3| engages a gear 48 which is suitably journalled in theplate 46, and a shaft 49 is extended from the gear 48, this shaftcarrying at its outer end a dial 50. is preferably divided into onehundred parts, of which each tenth division has been indicated on thedrawings. The gear 30 is also adapted to mesh with a pinion which isjournalled at the hub portion 52 (Figure 3) in the plate 45, this hubportion being extended as a shaft 53 which carries a dial 54, preferablymarked off in divisions, zero to 50. The dials 50, 54 are placedside-by-side in the same plane and quite close together so that theindications of the inner portions of the dials may be simultaneouslyread through a glass window 55, secured in a rubber bezel 56 (Figure 4)A consideration of the gearing in Figure 5 will show that as the handwheel 45 is rotated the pinion 4| will drive the gear 30 at a stepdownspeed, and assuming that the number of teeth on the pinions 4| and 5| isequal, the gear 30 will cause the pinion 5| to rotate at the same speedas the pinion 4| and the hand wheel 45. Thus the dial 54 will turn atthe same rate as the hand wheel 45. However, the pinion 3|, which hasthe same speed of rotation as the gear 30, drives the gear 48 at arelatively slow speed and the ratio between the number of teeth on thepinion and the gear is such that the dial 50, which is operated by thegear 48, is rotated The dial in at one-fiftieth the speed of the dial54. Thus the gearing is such as to cause the number dial 50 to rotatefifty times slower than the counter dial 54 for a given type of device,and the construction of the gear 30 is such as to prevent substantiallyall back lash between this gear and either of its pinions 4|, 5|. 'Whenthe hand wheel 45 is rotated the plunger 2| is reciprocated at a ratedependin on the speed of rotation of the hand wheel and its direction ofrotation, and the movements of the hand wheel are translated into exactreciprocatory movements at the plunger 2|. The indication at both dialsmay be readily seen through the window 55.

All of the parts of the wave meter described hereinbefore, including thegearing and with the exception of the wheel 45, are contained in awooden case 51, preferably of oak and varnished on its exterior surface.The Wooden case is extended about the four sides and the bottom but withthe top open to receive a panel 58 of a suitable insulating materialsuch as hard rubber. The bezel 56 is preferably provided with a flange59, which extends over and bears against the outer surface of the panel58. This panel is held in place on a metal plate 60 by means of machinescrews 6|. The sides of the box which form the outer casing are heldtogether by means of small angle iron pieces 62, one of which is shownat the upper left-hand corner in Figure 4 as being secured to the metalplate 60 by a screw 63. The other leg of the angle iron member isfastened to the wooden side 64 by a wood screw 65. There is a layer ofcopper 65 extending over the inner surfaces of the wooden sides, thecorner portions of each copper plate being inserted between the angleiron' 62 and the wooden side, thu being maintained rigidly in position.The purpose of the copper layer or sheet is electrically to shield theinternal parts of the casing from any external fields, magnetic orelectrostatic, so that the changes in electrical characteristics broughtabout by the movement of the plunger 2| are entirely free fromdeleterious effects.

In addition to the use of a copper plate for shielding purposes, stillanother shield may be optionally employed about the aluminum castingwithin the wooden casing. As shown in Figure 8, the casting may becoated with paint or enamel of any suitable and well known type, whichdries with a hard exterior surface but leaves a wet layer next to thealuminum casting. The purpose of the wet layer is to provide aconducting path of relatively high resistance around the aluminumcasting between the input and output terminals, so that any leakage highfrequency currents which tend to pass directly between the inputterminal 5 and the output terminal ll around the metal casting will bedissipated as heat in the resistance path formed by the interior layerof the paint or enamel. In Figure 8 the paint or enamel layer has beengenerally designated 51, of which the hard exterior layer is indicatedat 68 and the wet interior layer at 59, these layers being separated bya dot and dash line.

The wooden side 64 nearest the input terminal 5 is provided with anopening l0 which receives a circular cup-shaped member ll, madepreferably of bras or aluminum, the member being provided with a flangewhich bears against the outer surface of the wooden plate, as shown'inFigure 4. The bottom of the cup-shaped member is provided with anopening 12 which is sumciently large to snugly receive the threadedcollar I. The purpose of member II is to prevent energy passing aroundthe outside of housing I to output electrode I8 and circuits associatedtherewith. The terminal 6 is provided with a shoulder I3, upon which thecopper plate 56 and the bottom portion of the member II rest. The

"nut 9 presses the copper plate 65 and the member II tightly against theshoulder I3. The clamping effect exerted by the nut 9 closes all of thecrevices or cracks at this point through which otherwise ultra-high Ifrequency currents may leak. A handle 14 may be secured by the clips I5,which are screwed to one of the wooden sides of the casing forconvenience in transporting the instrument.

The circuit for the improved instrument is shown in Figure 9, and forclearness the various elements of the instrument are indicated by singlelines. Thus the copper layer 66 is shown as a vertical and horizontalline, grounded at 16, and the input; terminal 6 which contains the inputstub H is shown as passing through the copper layer. The aluminumcasting I is diagrammatically indicated as a rectangle, and thecapacitance or condenser effect existing between the lower end of theplunger 2| and the cylinder I9 is represented by a variable condenser11. The output stub is designated I8, as in Figure 4, this stub beingcarried through the conductor H to the grid 18 of a diode detector tube19. The plate 80 of the tube is connected to the grid through aconductor 8|, and these two electrodes are connected through a resistor82, by a conductor 83, to the control grid 84 of a high gain. amplifiertube 85. The conductor 83 is preferably shielded throughout its lengthby a copper braid 86, and the conductor is grounded as at 81 through aresistor 88. Th cathode of the tube I9 comprises a filament 89, one legof which is grounded as indicated at 9!), the other leg 9| beingconnected to a corresponding filament terminal of the cascade-connectedamplifier tubes. The auxiliary grid 92 of the tube 85 is connectedthrough a fixed condenser 93 to one leg of the filamentary cathode 94,this leg being grounded as indicated at 95. There is also a resistanceconnection indicated at 96 between the grid -92 and th'e B+ terminal ofa battery, which preferably is of the dry cell type. The anode 91 of thetube 85 is connected through a conductor 58 and a resistor 99 to the B+side of the battery, the lower terminals of the resistors 95 and 99being connected together as indicated at IIl'D.

The amplifier 35 is capacitively coupled through a condenser IllI to thecontrol grid I02 of a second high gain amplifier I03. The filamentarycathode is indicated at I04, having one leg grounded at I05. The controlgrid I02 is also grounded through a, resistor I06. The auxiliary gridIn! is connected through a conductor I08 to th'e B+ side of the highpotential battery. It will be noted that one leg of the cathodes B9, 94and IE4 is connected through a common conductor I09 to the A+ side of arelatively high current dry cell battery. The plate I") of the lastamplifier tube I03 is connected through a conductor III to one end of atransformer priinary IIZ, the other terminal of which is connected tothe B+ side of the battery. A direct current blocking condenser H3 isinserted in an extension of the line I II and a telephone jack I Id ofany suitable and well known type is connected to the extension line, asindicated. The secondary H of the output transformer is shunted by anadjustable high resistance IIB provided with a movable tap 1. This tapis connected through a conductor H8 to one corner of an asymmetricresistance bridge circuit for example a rectifier bridge shown at I IS,the opposite corner of which is connected through a conductor I26 to thelower terminal IZI of the transformer secondary. Copper oxide resistorshaving a forward resistance of to 1000 ohms have been usedsatisfactorily in the bridge circuit. It will be understood, however,that the resistance values are selected in accordance with'thecharacteristics of the associated components of the amplifying circuitand that th'e invention is not limited to specific values. One of theintermediate terminals of the bridge circuit is grounded at I22 and isalso connected to a, zero-to-200 micro-ampere scale ammeter I23. Theother terminal of the meter is connected through a conductor I24 to anintermediate terminal on a double-throw switch I25, the blade of whichis indicated at I26. The right-hand terminal I21 of the double-throwswitch is connected through a conductor I28 to the remainingintermediate corner of the bridge H9, and the left-hand terminal I29 isconnected through a conductor I3ll to the junction ILH of th resistor 82and the conductor 83.

Operation of the instrument and circuit Assume that a source ofmodulated ultra-high frequency waves of unknown frequency is connectedto the conductor Ia. These high frequency currents will pass to theinput stub II and will excite currents in the resonant circuitcomp-rising the aluminum casting I and also in the plunger 2| and itsassociated cylinders IS and 22, energy being stored alternately in theinductive and electrostatic fields of said circuit. The inductivereactive component of this circuit remains substantially constant, thecontrol of the resonance of the circuit being vested almost entirely inthe variable capacitative effect which is exercisedbetween the lowersurface of the movable plunger 25 and th' upper or nearer surface of thecylinder I9. In passing through the resonance'chamber comprising thealuminum casting, and the variable lumped capacity constituted by theplunger ZI and the cylinder It the high frequency currents excitecorresponding currents in the output stub I8 and are applied to thecombined grid and plate of the detector tube 19. At this point theoscillations are rectified and the modulation frequency components aresuccessively amplified by the tubes 85, I03. The output of the lastamplifier stage may be indicated at the telephone jack IM but it ispreferred to pass the output currents through the transformer to thebridge I I 9. When the switch blad I26 makes contact with the terminalI21 amplified currents are passed through the bridge to the microammeterI23. If the unknown signal is unmodulated, the blade I26 is turned tomake contact with the terminal I29, and the ammeter I'23 will thereby beconnected directly to the detector 79. In this case the direct currentcomponents are not amplified but are received directly by the meter.

For making the test for frequency, assume that the apparatus as a wholehas been properly calibrated. The hand wheel 45 is rotated to cause theplunger 2! to recede from or approach the cylinder I9 until a maximumreading is observed at the microammeter I23. It is obvious that underthese conditions the movement of the plunger 2| places the resonancechamber I in tune with the ultra-high frequency currents, and the exactvertical position of the plunger 2| by which this result is accomplishedmay be read as frequency or wave length by the two dials 5E}, 54. Thedial fi l may be considered as giving a unit reading between themultiple indications of the dial The reading of both dials may beobserved through the single glass window 55 which is mounted on the faceof the instrument, as shown in Figure 1. Th meter I23 is mounted on thetop cover of the casing, and in addition to the two indicators and thehand wheel there is a telephone jack H4 and an on-and-off switch I32connected in the filament conductor IdQ, also a knob I33 for varying theresistance IIB, and finally a knob I34 which is connected to the switchblade I26.

t is apparent that the face of the instrument contains only the minimumamount of apparatus, including the adjustment devices, so that theoperation of the instrument as a whole is fairly simple. The casing 57is sufficiently large to contain all of the necessary batteries, whichare preferably of the dry cell type to increase their portability. Thecompactness of the instrument is clearly shown in Figure 2. Thebatteries are conveniently placed in one corner of the casing, and thetransformer contained in a shielded case I35 is secured to and wellinsulated fro-m the top cover 60 of th casing. The variable resistor H5and the switch I25 are also conveniently mounted on the top cover, andthe latter in addition supports the resonance chamber I. It ispreferrred to mount the detector "I9 and the amplifiers 85, IE3 ondifferent sides of the resonance chamber. In Figure 2 the detector isshown as being contained in a metal casing Itt secured to the front sideof the chamber I, while the two amplifiers 35, I63 are contained in ametal casing IS! on a different side of the container, the two casingsbeing interconnected by suitable wiring, not shown in Fig. 2. All of thebattery leads, indicated at I3 3, are taken from their respectivebatteries through insulated cables to a removable adapter I3e, which hasprongs (not shown) making contact with sockets contained in a basemember I40 secured to the amplifier casing. It is apparent that bymoving the adapter I39 all battery connections are broken at the baseI48.

From the foregoing it is evident that I have disclosed an improved wavemeter which is adapted to measure either the frequency or wave length ofhigh frequency oscillations which may be generated, for example, in ahigh frequency tube oscillator. The connections between the conductor II and the oscillator may be made in any suitable and well known manner,such as by means of a loop dipole, capacity or a direct connection.Energy from the stub I I sets up oscillations in the resonator whichreach a peak valve when the tuning adjustment; exercised at the wheel 45and carried through the plunger 2| and the cylinder I9 is in tune. Thechamber I may be considered as a variable impedance and having a highimpedance at resonance frequencies. The inductance of the circuit is atleast approximately equivalent to a one turn toroidal coil. Thecapacitance is mainly concentrated between the elements 2| and I9. It isapparent that the free end of the plunger 2| and the cylinder It may beshaped to present to each other an increment of area variable inaccordance with any predetermined function as the portions are movedrelatively. For example, assuming that the lower end of the plunger 2|is fiat, the cylinder I9 could be given a contour at the edge whichwould cause a straight-line function between the instantaneous positionof the plunger 2| and either frequency or wave length of the currents towhich the chamber has been attuned. Thus dials fill and 56 may becalibrated in either frequency or wave length, depending on the shape ofthe edge surface at the cylinder I9.

It will be further noted that, due to the eliminaticn of substantiallyall back lash by the antibacklash gear formed of the sections 34, 35 andthe compression effect exercised at the spring 33, a direct and positiverelation is established between the instantaneous positions of theplunger 2| and the indications of that position shown by the dials 50,M. Thus the improved instrument has a hi h degree of resettability sothat the wave meter could be used for many years and still 0perateaccording to the calibration curve which had been determined by themanufacturer. This consideration is very important in connection withmeters which measure ultra-high frequency such as in the range of 300 to700 megacycles.

The concentric arrangement of the plunger 2| and the cylinder I9 is suchthat a movement of the plunger affects solely the capacitative elementof the resonant circuit because the mutual inductace between the centralcylindrical portion 22 and the outer casting I remains substantiallyconstant regardless of the position of the plunger. Consequently, themovements of the plunger 2| introduce only a .capacitative change in thecharacteristics of the resonant circuit, and this capacitance is lumpedat one general point free from any deleterious magnetic or electrostaticeffects and controllable solely by the operation of the hand wheel 45.As will be seen from Fig. 4, the electrodes Ill and I8 by which th inputand output are capacitatively coupled with the resonant circuitcomprising the housing I, the plunger 2| and its associated cylinders I9and 22 are located out of the primary field of the lumped capacitybetween the plunger 2| and cylinder I9 and hence provide a loosecoupling with the circuit. The term loose coupling is herein used tomean a coupling that is below a critical value below which the meterwill respond to only a single frequency for each position of the plunger2|. This loose coupling contributes to the sharpness of resonance of thecircuit since it does not introduce into the circuit external impedancethat would impair sharpness of resonance. It also avoids any materialreactance of the resonant circuit of the meter on the input circuit andany material reactance of the output circuit on the resonant circuit inthe housing I. It is hence possible to change tubes in the outputcircuit without materially affecting the calibration of the meter.Moreover, the movement of the plunger 2| to vary the lumped capacitancebetween the plunger and the cylinder I9 does. not materially change thecoupling of the input or output electrodes, and hence does not introduceerror.

While I have described the improved instrument as being adapted tomeasure the frequency or wave length of ultra-high frequency,oscillations, it will be understood that the instrument, if desired, maybe designed to measure frequencies in the lower frequency ranges. Properchoice of the pitch of the threaded control shaft 28, size of the gears3E3, Ill, 43, 5|, dimensions of the chamber I and cover plate 2 of thevariable capacity elements 2|, I9 and the shape of the curve of thecylindrical element I9 and the movement of the variable capacity plunger2| mayall be so designed that the range of frequencies over which theinstrument will accurately respond may be considerably changed. However,the improved instrument has an important advantage over otherinstruments, particularly in the ultra-high frequency range, ofresponding to only one frequency as determined by the maximum reading atthe meter I23, and positively will not respond to any harmonic orsub-multipl frequency, as is the case in instruments operable on theLecher wire principle. The instrument operates on the principle ofmaximum current reading rather than null current reading, and thusintroduces additional accuracy into the determinations.

If it is desired to cover a band of frequencies including 700megacycles, housing I should be about 2 /2 inches wide as viewed in Fig.4 and the other dimensions should be in proportion as illustrated. If itis desired to measure higher or lower frequencies, the dimensions ofhousing I and parts included therein should be varied substantially inproportion to the wave length of the frequency to be measured.

However, at frequencies below 700 megacycles it may be desirable to makestub electrodes l I and I 8 proportionately larger or to position themcloser to cylinder 22 in order to increase the capacity therebetween.Conversely, at frequencies above 700 megacycles these electrodes may besmaller or they may be spaced further from cylinder 22. In general morecapacity between the stub electrode and cylinder 22 will make theinstrument more sensitive but its calibration will then be changed morewhen tube 19 is replaced by one having different interelectrodecapacity, or when the capacity of conductor I4 is changed. Thus theexact size and position of the stub electrodes will depend upon theaccuracy and sensitivity requirements. As used herein, the term stubelectrode means the insulated terminal of a conductor arranged in moreor less close juxtaposition to another conductor to form an electricalcapacity therebetween. The term electrical capacity is used in a generalsense in this paragraph since some energy may be transferred between thestub electrode and other circuit elements by radiation or by inductivecoupling.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A wavemeter for measuring ultra-high frequencies comprising anelectrically resonant chamber including a closed metal container, afirst metal portion secured to and projecting inwardly from one wall ofsaid container, 9. second metal portion secured to and projectinginwardly from the wall approximately opposite said first metal portionto form a lumped electrical capacity therebetween, the free ends of saidmetal portions being oblique and shaped to present to each otheranincrement of area variable in accordance with a predetermined functionas said portions are moved relatively, means for changing the resonancefrequency of the resonant circuit thus formed by said container and saidportions comprising means for moving the free ends of said portionsrelatively toward and away from one another, and coupling meanpositioned within said container for applying unknown frequencies to theresonant chamber and for withdrawing the oscillations from the resonantchamber for indicating. resonance, said coupling means includinginsulated input and output electrodes projecting through the walls ofsaid chamber on opposite sides of said metal portions, and incapacitative coupling relationship with at least one of said portions.

2. A wavemeter comprising an ultra-high frequency resonant circuitformed of a closed metal container forming a cavity, a first metalmember projecting inwardly from one wall of said container, a secondmetal member projecting into said cavity from the approximately oppositewall of said container and concentric with said first member, a thirdmetal member movably supported by one of said other members andconcentric therewith to form with the other of said members a lumpedelectrical capacity, the extended ends of said two first-mentionedmembers being shaped to present to each other an increment of areavariable in accordance with a predetermined function as they are movedrelatively, means for changing the resonance frequency of the resonantcircuit thus formed by said container and said members comprising meansfor moving the free ends of said members relatively toward and away fromeach other, means comprising an input stub electrode which passesthrough said metal container for applying oscillations of unknownfrequency to said resonant circuit, means comprising an output stubelectrode which passes through said metal container for withdrawingoscillations from said resonant circuit, and means for measuring thewithdrawn current to indicate resonance. I

3. A wavemeter comprising an ultra-high frequency resonant circuitformed of a closed metal container, a cup shaped metal member projectinginwardly from one wall of said container, a cylindrical memberprojecting inwardly from the approximately opposite wall of saidcontainer and concentric with said cup shaped member to form therewith afixed electrical capacity, a metal plunger member movably supported bysaid cylindrical member for the greater portion of its length and forminwith said cup shaped member a lumped electrical capacity, the extendedends of said two last mentioned members being shaped to present to eachother an increment of area variable in accordance with a predeterminedfunction as they are moved relatively, means for changing the resonancefrequency of the resonant circuit thus formed by said container and saidmembers comprising means for moving the plunger member relatively towardand away from the cup shaped member, means comprising an input stubelectrode which passes through said metal container for applyingoscillations of unknown frequency to said resonant circuit, meanscomprising an output stub which passes through said metal container forwithdrawing oscillations from said resonant circuit, and means formeasuring the withdrawn current to indicate resonance.

4. A wavemeter comprising an ultra-high frequency resonant circuitformed of a closed metal container, a tubular metal member secured toand projecting inwardly from one wall of said container, a cylindricalmetal member secured to and projecting inwardly from the approximatelyopposite wall of said container and concentric with said tubular memberto be received therein and to form therewith a lumped electricalcapacity, the extended end of one of said members being shaped toterminate in a surface oblique to the common axis of said members, meansfor changin the resonance frequency of the resonant circuit thus formedby said container and said members comprising means for moving the freeend of one of said members toward and away from the other of saidmembers, and means positioned within said container for looselycouplingsaid resonant circuit to a source of unknown frequency and also to aresonance indicating apparatus, said coupling means including insulatedinput and output electrodes arranged on substantially opposite sides ofsaid members, and outside the primary field of said lumped capacity.

5. A wavemeter of the coil and condenser type, comprising an ultra-highfrequency resonant circuit formed of the following elements incombination: a closed metal container, a tubular metal member secured toand projecting inwardly from one wall of said container, a cylindricalmetal member projecting from the approximate opposite wallconcentrically with said tubular member and projecting int-c said memberbut out of physical contact therewith to form a lumped electricalcapacity therebetween, means for changing the resonance frequency of theresonant circuit thus formed by said container and said concentricmembers comprising mechanical means relatively mOVing said members tomove said cylindrical member into and out of said tubular member,frequency indicating means responsive to the relative position of saidmembers, and means including stub electrodes which extend from oppositesides of the container approximatel midwa between the ends thereof andare spaced from said cylindrical metal member for applying oscillationsof unknown frequency to the resonant circuit and for withdrawingoscillations from the resonant circuit to be measured by a resonanceindicating apparatus.

6. A wavemeter of the coil and condenser type, comprising an ultra-highfrequency resonant circuit formed of the following elements, incombination: a closed metal container, providing a cavity bounded on allsides by fixed wall surfaces, a tubular metal member secured to andprojecting inwardly from one 'wall of said container, a cylindricalmetal member projecting from the approximately opposite wall concentricwith said tubular member and projecting into said member but out ofphysical contact therewith to form a lumped electrical capacitytherebetween, a threaded shaft meshed into a threaded hole along thelongitudinal axis of said cylindrical member, control means accessiblefrom the exterior of said container for rotating said shaft to move saidcylindrical member into and out of said tubular member to vary theresonance frequency of the resonator formed by said container and saidconcentric members, frequency indicating means responsive to rotation bysaid shaft, means including an input electrode for applying to saidresonant circuit oscillations of unknown frequency, and means includingan output electrode for withdrawing oscillations from said circuit andapplying the withdrawn oscillations to a resonance indicating apparatus,said electrodes being arranged in juxtaposition with said members onopposite sides thereof, and outside the primary field of said lumpedcapacity. '7. In combination, an ultra-high frequency wavemeter of thecoil and condenser type, comprising a metal housing substantiallycompletely surrounding an adjustable condenser providing lumpedcapacity, said housing providing a cavity bounded on all sides by fixedwall surfaces, forming with said condenser a resonant circuit, means forindicating frequency, means for varying the capacity of said condenserand actuating said frequency indicating means, means including an inputstub electrode for applying oscillations of unknown frequency to theresonant circuit, and means including an output stub electrode forwithdrawing oscillations from the circuit and applying the same toresonance indicating apparatus, said electrodes being arrangedsubstantially in line with one another in a plane longitudinallybisecting said housing and in capacitative coupling relationship withsaid adjustable condenser but outside the primary field thereof andbeing insulated from said condenser and from said housing, said housingserving as a substantially complete shield for the resonant circuit ofwhich it is a part.

8. In an ultra-high frequency wavemeter of the coil and condenser type,the combination of a resonant circuit comprising a closed metal housing,providing a cavity bounded by fixed wall surfaces, a fixed condenserelement provided on a Wall of said housing, a movable condenser elementinside said housing and cooperating with said fixed condenser element toprovide a variable lumped capacity, said closed housing forming asubstantially complete shield for said circuit and providing with theelements therein inductance of said circuit, coupling elements comprisinconductors passing through and insulated from the wall of said housingand extending into said cavity for coupling said resonant circuit withan input circuit, the frequency of which is to be measured, and with anoutput circuit including means for indicating maximum energy output,said coupling elements being located outside the primary field of saidcondenser and providing a coefiicient of coupling sufficiently low thata change of impedance in the input or output circuit does not materiallychange the frequency of response of said resonant circuit, means formoving said movable condenser element to vary said lumped capacity whilemaintaining said coupling coeflicient substantially constant, andfrequency indicating means responsive to movement of said movableelement.

9. In an ultra-high frequency 'wavemeter of the coil and condenser type,the combination of a resonant circuit comprising a closed metal housingproviding a cavity bounded on all sides by fixed wall surfaces,relatively movable condenser elements disposed inside said housing andelectrically connected therewith, means for moving said condenserelements relative to one an-- other, frequency indicating meansresponsive to the relative movement of said condenser elements, thecondenser element forming a variable lumped capacity and having theedges thereof relatively contoured to produce a substantially straightline function between the movement of the elements relative to oneanother and the reading indicated by the frequency indicating means,input and output conductors loosely coupled with said resonant circuit,and means connected with said output conductor to indicate maximumenergy output.

10. In an ultra-high frequency wavemeter, the combination of a resonantcircuit comprising a closed metal housing providing a cavity whollybounded by fixed wall surfaces, a cup-shaped condenser elementprojecting inwardly from one wallof said housing, a sleeve memberprojecting inwardly from the opposite wall of said housing intoproximity to said cup-shaped element, a plunger of lesser diameter thansaid sleeve and cup-shaped element movably supported by said sleeve forthe greater portion of its length and movable into said cup-shapedelement to form a variable capacity, means for moving aid plunger,

frequency indicating means responsive to the movement of said plunger,the extended ends of the plunger and cup-shaped element being relativelycontoured to produce a predetermined function between the movement ofsaid plunger and the reading of said frequency indicating means,coupling elements passing through the wall of said cavity ondiametrically opposite sides of said sleeve for coupling said resonantcircuit with an input circuit, the frequency of which is to be measured,and with an output circuit including means for indicating maximum energyoutput, and insulating means between said coupling elements andsaidhousing, said coupling elements being located outside the primary fieldof said condenser.

STEPHEN D. LAVOIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,137,435 Yolles Nov. 22, 19382,251,085 Unk .Q. July 29, 1941 2,281,550 Barrow May 5, 1942 2,106,713Bowen Feb. 1, 1938 2,245,138 Zottu June 10, 1941 2,086,615 GrundmannJuly 13, 1937 2,095,990 Lindenblad Oct. 19, 1937 2,218,923 Newhouse Oct.22, 1940 2,235,521 Higgins Mar. 18, 1941 2,323,201 Carter June 29, 1943OTHER REFERENCES Natural Oscillations in Electrical Cavities, by Barrowand Miehers; Proc. IRE, April 1940, pp. 184-191. Copy in Division 51.

Cavity Resonators, by Terman, Handbook of 20 Radio Engineers, pp.264-273. McGraw-Hill Co.

1943. Copy in Division 51.

